This invention relates to high-intensity-discharge lamps and, more particularly, to such a lamp which utilizes a special discharge-sustaining filling of predetermined proportions of mercury and cadmium, in addition to a red-emitting phosphor coated on the protective envelope, in order to provide excellent color rendition of illuminated objects.
High-pressure mercury-vapor lamps which have a light emission modified by the use of phosphor mixtures are well-known and one embodiment of such a lamp is described in U.S. Pat. No. 4,065,688, dated Dec. 27, 1977 to W. A. Thornton, the present applicant. The phosphors utilized include red-emitting yttrium vanadate or yytrium phosphate vanadate activated by trivalent europium. Another embodiment of such a lamp is described in U.S. Pat. No. 3,602,758, dated Aug. 31, 1971 to Thornton et al.
A method for preparing red-emitting yytrium vanadate phosphor activated by trivalent europium is disclosed in U.S. Pat. No. 3,630,946, dated Dec. 28, 1971 to Ropp et al and such phosphor is now well known.
It is known to use cadmium vapor as a discharge-sustaining medium in a fluorescent lamp, as taught in French Pat. No. 1,488,562 Del. Date June 5, 1967.
Cadmium-mercury amalgams have been used as discharge-sustaining medium in highly loaded fluorescent lamps, as disclosed in U.S. Pat. No. 3,263,111, dated July 26, 1966.
Cadmium has been used as the discharge-sustaining constituent in high-intensity discharge lamps, as disclosed in U.S. Pat. No. 3,657,590, dated Apr. 18, 1972.